In small change this week I acquired a Charles Darwin £2 coin

I was delighted this week to receive a Charles Darwin £2 coin in my change when shopping.

The coin was struck by the British Mint as a limited edition in 2009 to mark the bicentenary of Darwin's birth. It depicts a profiled head of the great man face to face with a chimpanzee.

Although legal tender, the Darwin £2 coin is rarely found in small change:

"Its rarity means that, in mint condition it is worth three or four times its face value. Even a used coin is worth double its tender value. The price acceleration means that it is well worth seeking out as an investment."

Another Darwin coin was issued in 22 carat gold. This is not in circulation although it, too, is legal tender. Most are in the hands of coin collectors.

When I was stationed in Spain while in the US Navy, I would frequently take car trips to Gibraltar. The first trip I took, I noted what is on the back of the £10 note, compared to the back of a US$10 note: